How To Cut Fiberglass

By Mark Corke

When you must cut into your boat to install equipment, use the right tools and techniques for a neat, professional-looking job.

I well remember the first time that I had to cut a hole in my new boat. I'd just bought a compass that needed to be fitted into the bulkhead next to the companionway, and I was nervous — very nervous. What if I messed up? What if I made the hole in the wrong place?

In the end, the job worked out just fine, and since those early days, I've drilled and cut countless holes, and I've learned some lessons along the way. As with everything in life, preparation is key, and a positive, can-do attitude is almost as important as having the correct tools. Taking your time and thinking the job through help to make sure that it turns out as intended while reducing fuss and frustration. A hole is a hole; the one we'll cut here is intended for a new VHF radio. But the same process applies to anything that needs to be fitted into a console or other fiberglass panel: a stereo, a depth-sounder display, a chartplotter, a fishfinder, a compass.

  • Photo of cutting out a paper template
    Photo of tracing the template onto the fiberglass

1. Most electronics come with a template in the box. Use masking tape to position the template. Examine this from several different angles. Is it level? Will you be able to operate all the controls once it's in place?

2. Once you're happy with the placement, draw a line around the inside of the template with a pencil or marking pen, take a deep breath, and move on to the cutting stage.

  • Photo of template ready to drill
    Photo of saw blades

3. Using the correct tools helps ensure success. Almost without exception, the cutout for any equipment will be rounded at the corners, and for that, a drill is required Choose a drill bit based on the required radius for the corners. In most cases, a sharp twist bit is all that's needed, but a hole saw can be used if the radius is large. A rechargeable electric drill makes short work of the task.

Drill carefully through the fiberglass at each corner. Usually, you can eyeball where the point of the drill needs to be placed before drilling the hole. But a few measurements and a pencil mark will do the trick if you lack confidence. Aim to be as accurate as possible, while being careful not to creep outside the line. Better to be inside the line, if anything, as you can always cut a little more out if necessary.

4. With drilling completed, the next step is to cut between the holes. There are several ways to accomplish this, but my first choice is to reach for a jigsaw fitted with a fine metal-cutting blade. Whatever you do, don't use a coarse blade intended for use on wood. The fiberglass will vibrate, you'll chip the surface, and you could crack the fiberglass laminate. The thinner the fiberglass, the trickier it can be to cut because it will flex and, without care, may crack.

Photo of cutting the fiberglass

5. Insert the blade into the hole; make sure the base plate is clean and smooth and firmly in contact with the gelcoated surface before pulling the trigger. Cut slowly and steadily just a fraction inside the line, repeating the procedure between each of the holes.

Photo of fitting equipment into hole

6. After cleaning up any mess, fit the equipment into the new hole. If it's a little tight, you may need to ease the opening with a suitable file.

Photo of the radio screwed into place

7. The radio came with a neoprene gasket, which was installed between the back of the unit and the front face of the console. Screws from the rear hold the radio in place and complete the installation.

Decide where the equipment will be installed. In many cases, choice will be limited, but try to avoid installing any electrical equipment too close to the compass, as most if not all electrical components will cause deviation in the compass heading. Before you cut, examine not just the face of the console but also what's on the other side. You don't want to slice inadvertently through cables that are hidden from view. Also, ensure that you'll have room to make all the necessary connections once the unit is installed. Our console was made from solid fiberglass, but if cutting through cored material, the edges of the core should be sealed with epoxy, after completing the cut, to prevent water ingress 

— Published: Fall 2015

Take Precautions

Working with fiberglass is unpleasant at best, so use adequate precautions. Wear gloves, a dust mask, goggles, and a long-sleeved throw-away shirt to avoid coming into contact with the dust. Vacuum up dust immediately to avoid tracking it all over the boat.

Photo of safety gear need to work with fiberglass



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